1. The 'top hat' shim or 'lash cap is often used to take up the clearance that is created when changing from standard cams to competition cam. Competition cams often have a smaller diameter base-circle. Top hats just sit on the valve tip with a good, but not necessarily tight fit. Best material is alloy steel like En36 which contains nickel and case-hardens well to say 15 thou deep, allowing for finish grinding, and thus resists wear without becoming too brittle.
Top-hats must not bear against the collets or the fretting will severly damage the valves and spring caps. Fitting requires great care - always do a dry run without them and take measurements then fit them and re-measure. If the clearances are not reduced by the thickness of the top-hat, one has become dislodged.

2.Identifying the different sections of the camshaft. This is a Fiat 8v TC cam, where there are no separate bearings, the cam runs direct in the housing.